1. Field of the Invention
The present invention relates generally to an integrated circuit test fixture and method incorporating fluid cooling of the integrated circuit during testing. More particularly, it relates to such a fixture and method which utilizes a high thermal conductivity gas and/or a cooling fluid. Most especially, the invention relates to such a fixture and method which will allow high powered integrated circuits to be tested while running the integrated circuits continuously prior to being separated from a wafer. In particular, the invention relates to an improved form of the fixture and method described in the parent application.
Like the fixture and method described in the parent application, the present invention is meant to cool wafers or other flat components while they are generating heat. When the wafers are being powered, they must be cooled to prevent damage or to operate at specific temperatures. The amount of heat that is generated can be greater than that which may be handled by conventional wafer-cooling chucks. This invention increases the amount of heat that may be removed from a wafer.
2. Description of the Prior Art
High powered integrated circuit chips, such as emitter coupled logic (ECL) chips, require a large quantity of electrical power, which is converted and dissipated as heat. For example, at a typical power dissipation level of 30 watts/cm.sup.2 for ECL, the temperature of an isolated die will rise at 300 degrees C./second of applied power in the absence of any method to remove the generated heat. To enable testing while still in wafer form, pulsed power testing is often used. A die site on the wafer is probed, and power is applied only for a fraction of a second. There is some heat sinking to adjacent silicon of the wafer and to the wafer chuck of the probing station, so short tests can be run without burning up the chip.
More advanced ECL chips now under development, such as high speed microprocessor chips, will have a much higher watt density, such as almost 60 watts/cm.sup.2. In the future, integrated circuits having watt densities of 100 watts/cm.sup.2 or higher will be developed. Such microprocessor chips also will desirably employ a clocking scheme that would complicate designing the chip for pulsed power testing. It is therefore desired to run the chip continuously at full power during testing. Such a capability would be desirable in almost any ECL probing application.
It is known in the art to provide coolant fluids, such as an inert liquid that is boiled to remove heat from packaged integrated circuits. It is also known to use helium as a thermal conductivity enhancer between two members. It is further known to test such packaged integrated circuits and circuit boards by immersing them in the inert liquid. Such techniques have hitherto not been adapted for use in a test fixture for integrated circuits still in wafer form. It is further known to pass water through passages in a wafer chuck to chill the chuck, but the current state of the art does not remove enough power evenly from high power density integrated circuits to allow them to be operated at full, continuous power, with low, uniform operating temperature, because it is hard to get good enough thermal contact to exploit fully water cooling.
Conventional wafer cooling chucks operate by passing cooling fluid through large paths within large pieces of metal. The wafer is held down on this metal by vacuum. Such conventional wafer cooling chucks are made, for example, by The Micromanipulator Co., Inc. The thermal effectiveness of this chuck is hindered by several factors:
1. The gap between the wafer and the chuck, which the heat must pass through, is filled with air. The poor thermal conductivity of the air leads to large temperature drops across that gap.
2. The cooling liquid is spaced remotely from the wafer. The heat must therefore travel a substantial distance through metal to get to the cool liquid.
3. There are only a few cooling fluid paths, and they are relatively large in diameter. Such a structure does not provide a uniform heat sink.